The present invention relates to methods for assessing the quality of cereals.
It is known that different qualities of wheat are required for different applications. Bread-baking, for example, requires wheat which ensures that the dough rises a great deal and that a large bread volume is obtained. On the other hand, biscuits are preferably baked from wheat which provides doughs which are not as fluffy. Pasta-making, in turn, requires wheat which provides a dough which can be extruded, while wheat which is to be used as forage should have high forage functionality, i.e. result in large growth in the animals which are being fed.
In order to optimize the use of wheat and to produce finished products which are the best possible, it is thus important for users to be able to buy wheat of the right quality. This presupposes that the quality is known. However, the fact is that different types of wheat can be of different qualities, but the same types of wheat can also be of different qualities because of, for example, different growing conditions, different weather conditions and different fertilizing. Consequently, the quality must be assessed experimentally.
In Swedish grain depots, the quality of a shipment of wheat is normally assessed by a sample being taken from the shipment and its falling number, its water content and its protein content being assessed. Payment is then based on these values. However, this method is not completely reliable, since it does not always measure the quality of the wheat. For example, it is possible to increase the protein content by increased fertilization without improving the quality in terms of baking volume or forage functionality. Consequently, the quality assessment described above is often combined with test baking. However, test baking takes such a long time that the result cannot be used at depots for sorting shipments of grain by quality.
Accordingly, there is a need for a new method for assessing cereal quality.
A known apparatus, which is used in studies of the quality of wheat, is the mixograph, which is available from TMCO, 501 Jay Street, Lincoln, Nebr., USA. The use of the mixograph is described in the AACC Standard 54-40A.
In short, the mixograph comprises a bowl, in the bottom of which three pins are fixedly placed and in the lid of which four pins are movably arranged. The mixing bowl is mounted on a vertical shaft so that it can rotate around it. An arm is fitted to the bowl. In the one end of the arm a spring is attached, which extends perpendicular to the arm and which is fixedly anchored in the base of the mixograph. A pen is attached to the other end of the arm.
The mixograph is used as follows. A sample of wheat of which the quality is to be assessed is milled into flour and is poured into the bowl of the mixograph. Water is added. The flour and the water are mixed to form a dough by the movably arranged pins being caused to rotate around the fixed pins. Subsequently, the mixing of the dough continues for a predetermined period of time. In connection with the mixing, stress arises in the dough. The stress causes a torque on the mixing bowl. The torque is registered on a sheet of paper which scrolls forward at a constant speed under the pen. The curve obtained is called a mixogram and is used as an aid for assessing the quality of the wheat. Normally, the mixogram is studied visually, in which case mixograms of different samples are compared. It is also known to correlate individual parameters which are determined from the mixogram with measures of quality, such as baking volume or dough quality. The parameters mentioned in the AACC Standard are:
Peak time, i.e. the time it takes for the torque to reach the maximum level;
The area under the curve from the beginning of the mixing to a specified point in time;
Middle peak height, i.e. the maximum height in the middle of the curve; and
The angle between the ascending and the descending parts of the curve at the maximum torque.
So far, the mixograph has only been used in laboratories, and not in depots. In order to permit its use in depots, it must be possible to carry out the quality assessment in a short period of time. This is not the case at present, since the mixograph only produces curves which then have to be evaluated. Furthermore, a high correlation is required with the cereal quality which is to be assessed. A minimum level of 80-85% has been mentioned.
Other well-known apparatus for testing the quality of doughs are the farinograph, the extensograph and the alveograph, which are described in, for instance, an article by P. W. Heaps et al. xe2x80x9cThe rheological testing of wheat glutens and doughsxe2x80x9d, p. 1095-1096 in Chemistry and Industry, Aug. 10, 1968. These apparatus are likewise unsuitable for quality assessment at depots or other commercial applications where it is a requirement that the quality assessment can be carried out simply and in a short period of time.
In the article xe2x80x9cRelaxometriexe2x80x94ein neuer Weg zur Qualitatskontrolle von Lebensmittelnxe2x80x9d in Lebensmittel-industrie 29 (1982), the inventor of the present invention suggests that the viscous and elastic properties of semi-solid substances can be studied by means of stress relaxation. More specifically, a sample of the semi-solid substance is sheared between a cone and a plate, and a relaxing curve for the semi-solid substance is registered. The relaxing curve can be used for quality control of gluten in wheat. This known equipment is only used in laboratory tests and thus is not suitable for commercial use.
Naturally, the problems described above with respect to quality assessment of wheat also exist in the quality assessment of other cereals.
One object of the invention is thus to provide a new method, which can be used for assessing the quality of cereals.
Another object of the invention is to provide such a method and such an apparatus which can be used for quick and easy quality assessment of cereals.
A further object of the invention is to provide such a method and such an apparatus which can be used for quality assessment of cereals with a high degree of prediction.
Yet another object of the invention is to provide such a method and such an apparatus which are suitable for use in grain depots.
The above-mentioned objects are achieved by methods and apparatus which have the features stated in the appended claims.
The invention thus combines the known mixograph technique with the insight that valuable information about the quality of a cereal type can be obtained by studying how the stress in a dough, which contains the cereal in question, relaxes subsequent to the dough having been subjected to deformation. Mixing is a simple and known technique for achieving a dough and deforming the same. However, unlike in the known mixograph technique, the deformation is interrupted and the quality assessment is based on the stress in the dough when it relaxes. As a result, a very high degree of prediction can be achieved. Tests show that relaxing parameters correlate very well with the quality of cereals. For example, with three relaxing parameters a correlation of more than 88% with baking volume for wheat has been achieved.
Moreover, the fact that the deformation is effected by means of mixing and the mixing and the relaxing are effected in one and the same container, permits the quick and simple handling which is suitable for use in, for example, grain depots.
As was indicated in the introduction, the quality of a cereal type can be represented by, for example, a measure of the baking volume, a measure of the extrudability, or a measure of the forage functionality. It can also be represented by of a measure of some other quality characteristic, which correlates with one or more relaxing parameters.
The invention has been tested with very good results as regards wheat. It is presumed that it can be applied to other types of bread cereals, such as barley, rye, and oats, with equally good results. It is also presumed that the invention can be used for assessing the quality of rice, yams, cassava and other starch-based plants. Accordingly, when the term cereals is used in this application, it shall include these and similar products.
According to the invention, a dough is thus prepared by mixing the cereal type whose quality is to be assessed. When the cereal type is a grain, the dough is suitably made with flour from the cereal type and water. When the cereal type is not suitable for milling into flour, it can be worked in some other manner, e.g. it can be chopped, and liquid can be added.
The deformation of the dough, which consists of extensional strain, is preferably performed until the dough is fully developed, which it is considered to be when the stress in the dough reaches the maximum. Obviously, the deformation must continue for a short while after the maximum has been reached to make it possible to register that the maximum has been passed. The deformation can continue for about 1 minute after the maximum has been passed, since it is considered that the dough does not begin to break down until approximately this point in time.
Both the dough and the deformation of the same can be achieved by mixing in an apparatus which carries out mixing in the same manner as a mixograph.
According to the invention, the stress in the dough is registered. This can take place continuously or at selected times. If the stress cannot be measured directly, another quantity, which gives a measure of the stress, can be registered.
Furthermore, at least one relaxing parameter is suitably determined on the basis of the stress registered during the relaxing and is used in a predetermined calculation model. Since the relaxing parameter is to be used in a calculation model, a numerical value is determined for this parameter. The calculation model can preferably be a neural network which has been trained to perform the desired quality assessment for the cereal type in question. It can also consist of a linear relation which has been determined by means of, for example, multivariate analysis. A neural network can be expected to provide a somewhat higher degree of correlation since it can identify non-linear relations.
In a preferred embodiment, one lets the dough stand for a predetermined length of time subsequent to the interruption of the deformation. Subsequently, the dough is again deformed before the dough is allowed to relax. The deformation after the standing is preferably effected in such a way that the stress reaches a predetermined value, which can suitably be the value of the stress when the deformation was interrupted, i.e. close to the maximum stress. The advantage of letting the dough stand after the initial deformation is that this gives the dough time to xe2x80x9chealxe2x80x9d from some of the damage it receives during the deformation. This is assumed to lead to more certain results in the quality assessment. Alternatively, the relaxation measuring can be performed immediately after the first deformation has been interrupted.
The most certain correlation with the quality is obtained if the deformation, the relaxing, and the registration of the stress are repeated several times, and an average is established of the stresses registered as a function of time, the relaxing parameter being determined on the basis of the average relaxing curve. This possibility presents an advantage compared with the traditional mixing which can only be performed once.
It has been found that the following parameters are particularly suitable for assessing the quality of cereals. The absolute stress in the dough at a predetermined time subsequent to the interruption of the deformation, the relative stress in the dough, i.e. the absolute stress at a predetermined time subsequent to the interruption of the deformation divided by the maximum stress, the maximum on a curve of the derivative of the relative stress as a function of the logarithm of time divided by the value of the relative stress at this point, and the slope of the curve of the derivative of the relative stress as a function of the logarithm of time in the final phase of the relaxing. In a multivariate analysis some of the parameters must be inverted.
The very highest degree of correlation with cereal quality has been obtained when the assessment of the quality has been based on one or more relaxing parameters in combination with one or more mixing parameters, i.e. parameters which are determined on the basis of the stress registered during the deformation. In such cases, a correlation of more than 92% with baking volume for wheat has been achieved.
A mixing parameter which has been found to be particularly useful is the so-called build-up parameter, which is determined as the difference between the maximum stress in the dough during the deformation and the stress in the dough at the point in time when all the liquid has been absorbed. This is an entirely new parameter which alone has a correlation of more than 80% with baking volume for wheat. It is presumed that it also has a high correlation with measures of quality for other cereal types. Since this parameter has such a high degree of correlation, it alone could be used for assessing quality. Accordingly, in this case, one would not need to effect any relaxing, but rather a traditional mixogram could be recorded, the build-up parameter be determined with the aid of a calculation unit and be used for quality assessment, e.g. in a predetermined calculation model. The advantage of this would be that no advanced calculation equipment would be needed. The build-up parameter can, of course, also be combined with other mixing parameters for improved correlation with cereal quality.
An apparatus for assessing quality based on relaxation contains means for preparing a dough by mixing a cereal type whose quality is to be assessed and for deforming the dough by mixing so that stress arises in the dough, as well as means for registering the stress in the dough. In addition, the apparatus has a calculation unit, which is adapted to assess the quality of said cereal type with the aid of the stress in the dough which has been registered during the relaxing of the dough subsequent to its deformation, the apparatus comprising a container in which both the mixing and the relaxing are effected.
In a preferred embodiment, the calculation unit determines a relaxing parameter on the basis of the stress registered during the relaxing and uses this relaxing parameter in a predetermined calculation model for assessing the quality.
Essentially the same apparatus as the one described above can be used for quality assessment based on the above-mentioned build-up parameter. However, in this case, no relaxing is performed, but instead the calculation unit calculates a mixing parameter by determining the difference between the maximum for the stress in the dough during mixing and the stress in the dough when all the water has been absorbed. This mixing parameter is used in the quality assessment.
Unlike the output signal from the known mixograph, the output signal from this apparatus is a direct measure, preferably a numerical value, of the quality of the cereal type examined. Accordingly, this apparatus is suitable for commercial use. It is easy to operate, since the process can be made completely automated. The user only needs to pour in suitable amounts of the cereal type which is to be quality assessed and of liquid.
In order to achieve the dough and the deformation of the same, the principle of the mixograph is preferably used, i.e. a container and a plurality of deformation members which deform different parts of the dough in different directions. The advantage of this is, inter alia, that the mixograph is a known apparatus which is available on the market.
By the methods and the apparatus according to the invention, the quality of different cereals types can be predicted with high accuracy by a simple and quick procedure. The invention can advantageously be used in depots, in which case a fairer price can be obtained for the farmers who have grown the cereals. Moreover, the invention makes it possible to bring out new qualities in cereals which are specially adapted to particular applications. The invention can advantageously also be used in bakeries, in the processing industry, in mills and like places where cereal quality needs to be assessed.